Protractor



c. HLITTLE Juny 2s, 1936.'

PROTRACTOR Original Filed April 1, 1931 4 Sheets-Sheet 1 C. H. LITTLEJuly 248, 193s.

PROTRACTOR Original Filed April 1, 1931 4 Sheets-Sheet 2 AJuly 2s',1936.

c. H. LITTLE PROTRACTOR 4 sheets-sheet s Original Filed April l, 1931Julyzs, 1936.

c. H. LITTLE f 2,049,302

PRoTRAcToR" Original Filed April l, 19:31

4 Shets-Sheet 4 Patented July 28, 1936 UNITED STATES .rATENT oi-Ficaapplication April 1, i931, serial No. 526,912 Renewed January 3, 1936 20Claims.

This invention relates to protractors and especially to a draftinginstrument consisting of a protractor with provision for receiving andholding rulers which are rotatable as a unit with the protractor plate.

The invention i'lnds particular utility in a protractor which visconnected to a drawing board with a suitable parallel motion mechanismsuch as that composed of a pair of parallelograms or of the jointed armtype known as Universal drafting machines covered by numerous patentsheretofore granted to me, among which I might mention Patent No.1,208,340, granted Dec. l2, 1916. The invention, however,` is notnecessarily cond iined in its use in connection with a parallel motionmechanism particularly of the kind referred to. l

The principal objects of the present invention are to provide improvedruler holding facilities, greater rigidity and accuracy, greaterconvenience in operation, a simpler and less expensive instrument tomanufacture, reduced number of parts, decreased Weight, improvedappearance, and automatic take-up for wear between certain of o theparts. Y

The above and other objectsare attained by the present invention, anembodiment of which is illustrated in the accompanying sheets ofdrawings which, for convenience in explaining the 30 construction andadvantages of my improved protractor, show the latter applied to adrafting machine of the Universal type.

In the drawings, f Figure l is a plan view of adrafting machine of theUniversal type applied to a drawing board; Fig. 2 is an enlarged planView of the protractor showing portions oi two rulers applied thereto intheir usual right angle relationship;

Fig. 3 is a view similar to Fig. 2 on a smaller 4G scale and with partsbroken away;

Fig. 4 is a bottom view of the protractor; Fig. 5 is a sectional viewsubstantially along the line 5-5 of Fig. 3;

Fig. 6 is a side view of the protractor with parts 1 broken awaysubstantially along the line 6--6 of Fig. 2; Y

Fig. 'l is a similar view with parts in section taken substantiallyvalong the line 1-1 of Fig. 2; Fig. 8 is a detail sectional viewsubstantially along the line 8-,8 of Fig. 2;

Fig. 9 is a transvese sectional view substantially along the line 9 9 ofFig. 2; Fig. 10 is a transverse sectional view through one of the rulersand through one of the two or more chucks carried' by the ruler as wellas the section may be assumed to be taken along line lil-i0 of Fig. 2.

Fig. 10a is a perspective view of `the under side of a short section `oione of the rulers;

Fig. 11 is a detached view of a notched plate which, for convenience,will be termed the holding plate, to the center of which the protractorplate ha's a ball pivot connection;

Fig. 12 is a sectional view taken substantially along the line |2l2 ofFig. 11;

Fig. 13` is a detached view of a chuck arm plate which, as will beexplained, is attached to the protractor plate and turns as a unittherewith; and v Fig. 14 is a sectional view taken substantially alongthe line iQ-M of Fig. 13.

As above stated, I have illustrated my invention in the protractorapplied to a drafting machine of the Universal type, this beingillustrated in Fig. 1, wherein ,the drawing board is designated i5. Themachine is secured to the board by means of an anchor i5 here shown as amidanchor, but, of course, any suitable anchor may be employed. As iscustomary in machines of this type, lthe jointed arm is attached to the`anchor through .the medium of an anchor plate i1 which, in thisinstance, is pivoted to the anchor to swing about an axis of about 60with the top edge of the drawing hoard. The upper parallelogram includesthe two parallel rods i8 and `the lower parallelogram includes thetwoparalel rods i9. The anchor plate il, which is detachably connected withthe anchor I6, forms the connecting member for the upper parallelogram,the rods i3 being pivoted thereto. At the joint between the two pairs ofparallel rods, an annulus 2i is provided to which the adjacent ends ofthe two pairs of rods are pivoted and the lower ends of the rods i9 arepivoted to a plate 22 which is an extension of and is secured to arms 23on the notched holding plate 2d, shown in Figs. 4 and 11. g l

The protractor includes three principal members which are stamped fromsheet metal. These consist of the protractor plate 25 which is acircular disk (see particularly Figs. 2 and 9), the chuck arm plate 26(see Fig. 13), and the holding plate 24 (Fig. 11). In the assembledprotractor,

the protractor plate 25 and the chuck arm plate 26 turn as a unit andreceive betweenthem the holding plate 24. In order that the protractorplate and associated chuck arm plate may be turned conveniently, theprotractor plate has secured to it centrally thereof by screws 21 awooden handle 28, the protractor plate having at its peripherygraduations 29 which cooperate with an indicating line on a member 3|)secured to the holding plate, the member 30 being in engagement with theperiphery of the protractor plate. The protractor plate, or rather theunit composed of the protractor plate and the chuck arm platey ispivoted for-rotary movement and accurately centered with respect to'.the .holdirig.plate 24 by a ball pivot 3| which is best illustrated inFig. 9. The manner in which this ball is supported and the parts held inproper relationship will be referred to presently.

Taking up next the holding plate 24 (Fig. ll) it will be observed thatthe major portion-of it is in the form of an annulus 32 'with notches 33at the outer periphery thereof for engagement with the nose of a ratchetpawl which is adapted to position the protractor plate in the anglesmost' commonly used- Inside this annulus there is an annular opening 34of somewhat less than 360 in extent, the'continuity ofthis"annulaopening being interrupted by an inwardly extending arm 35 on:the holding plate, the sides of'thev arm being tapered or inwardlyconvergent andl thev inner portion of this arm being oisetA downwardlysomewhat, as indicated at 35B. in Fig. 12

and being provided at the center of the holding 1 v tractor plate (seeFig. 9) which lies immediately above the holding plate and -at itsperiphery projects outwardly beyond the annular portion of the holdingplate so as to completely cover andy conceal the notches 33. Theportions of the protractor plate and holding plate which engage the ballare held -in close but practically frictionless engagement'with the ballby a spring plate 31 (see particularly'Figs. 4 and 5) whichprcfjectsfrom a portion of the chuck arm plate andl` engages under the inner endof the arm 35 of the holding plate and presses the same upwardly againstthe pivoting ball 3l and keeps the latter closely'seated inbeveled seatsof the protractor plate and'holding plate. While I regard it as-'within' the invention to make spring plate a the chuck arms are in oneunitarS1 stamping.

whichmay be formed ofstaimess steel, this being.

. t'o the best -of my knowledge, the rst instance wherein'the two chuckfor an instrument of this kind are formed integrallypf one pie'ce. As

will be observed from Fig. 13, the two chuck 39 and- 40 are, as usual,at right anglesto each other, these tw chuck arms being adapted toreceive rulers 4l and hold-them in their rightang'ular relationship in avery novel manner to be explained presently. One of the chuck arms e is,in this instance, longer than the other inas much asfit is customary.that what is termed the horizontal ruler, i. e., the-one held bythechuck arm 3 9, be longerv than what is-commonly called the verticalrulerwhich is held "by the chuck arm 4|).- The'two chuck armsand the portionsof the plate-"or stamping `adjacent thereto lie inv one plane and thebottom surfaces o'f these arms and the portion referred to may engagethe ing the center and'axis of rotation vof the proing paper held on theboard I5, but preferably they are very slightly above the lower surfacesof the rulers and therefore slightly above the drawing paper.

Next to the portion of the chuck arm plate which engages the'drawingpaper, as just explained, there is an arc-shaped upwardly oil'setportion 42, this being close to and, in fact, extending under theperipheral portions of the protractor plateand of the holdingplate 24and constituting a support for the ratchet pawl (to be referred topresently) which cooperates with the notches 33 of the holding plate.Next to the I upwardly offset portion 42 there is a substantiallyannular upwardly oiset portion 43 which engages the under surface of theholding plate 24 inwardly somewhat of the periphery of the latter, thisportion inthe assembled protractor being' concentric with respect to thecenter or pivotal axis of the protractor-plate. Inwardly of the upwardlyoffset portion 43 there is a third upwardly offset portion 44 whichextends inwardly of the annulus" 43 in the form of a arm having taperedsides and' embracing in'circu'mferential extent slightly more 25 than ofthe inner periphery of the annular portion 43. The upper surface of thisupwardly. offset portion 44 of the chuck arm plate hes at against thelower side of the protractor plate' and it is secured thereto by screws45. this portion 44 of the protractor plate that the spring plate 31 issecured by the screws 38, this spring plate virtually forming an oisetlextension of the portion 44 of the chuck arm plate.

Thus it will be seen that thev chuck arm through the medium of the'portion 44 thereof, engages the protector plate for a substantialextent with-the engaging portions firmly secured together so as tosecure 1these two plates together so that they will turn as a unit. Atthe same time there is obtained by the offsetting described, a bearingby the inner Vannular portion 43 on the 'lower' side ofthe holdingplate, the amount of the offsetting between the parts 43 and 44 being,"equal substantially to the thickness of the holding plate so that theprotractor plate and the chuck arm plate receive the holding platebetween them with a close iit but nevertheless one which allows thedesiredfreedomrof movement of the protractor plate and chuck arm plateunit. By'this It is t0 3gplate, 35

construction, assisted by the centralizing and holding action of thepivoting ball, the assembly has a high degree of rigidity, all looseplayds eliminated, and no relative movement permitted except 'thedesired rotary movement of the protractorplate' and chuck plate armabout the vertical axis vo f the ball pivot. Obviously also the numberof parts is reduced to a minimum.

An additional advantage of the ball' pivot formtractor plate on thenotchedbholding plate liesin the fact that it greatly facilitatesobtaining proper centers, l. e., bringing the protractor plate andholding plate in true central relationship 'with respect to each other.

Should the beveled 6;,

ball seat irreither plate be outjof alignment even the' slightestextent, it can be brought into exact' alignment by applying a lineremuer-, A to one of Athe beveled seats and slightly crowding it'toward' the side where the metal is to be removed. This 70 gives amethod of obtaining tru'e centers between plates having notches atcertain' angles and the graduated protractor plate. The' greatest difii'of the arm 35. Notwithstanding the fact that these portions of the twoplates are'in the same plane, by tapering their opposite sides asillustrated, the bases or relatively wide portions of these two inwardlyextending parts are sufficient in their circumferential extent to `givethe required rigidity, and at the same time, when the protractor is inzero position shown in Figs. 3 and 4, the oppositely disposed openingsor spaces between the inwardly projecting parts 44 and 35 (see Fig. 4)are somewhat more than 90 and consequently the protractor can be turnedor rotated through somewhat more than 90 in both directions from zeroposition, the protractor being preferably graduated through an arc of180.

Taking up next the ratchet pawl and its support, it will be noted thatthe rst upwardly offset arc-shaped portion 42 (Figs. 13 and 14) hasmounted on it the ratchet pawl 46, the pawl extending somewhatcircumferentially of the `pro tractor plate and its nose being adaptedto snap into any one of the peripheral notches 33 of the holding plate,the thickness of the ratchet pawl being such that it will have freedomof movement on the portion 42 of the chuck holding plate beneath theprotractor plate so that its nose may snap into any one of thesenotches. It is a fea- .ture of the present invention that this ratchetplate has a ball pivot 41 on the portion 42 of the chuck arm plate (seeFig. 8), the ball engaging beveled openings in the ratchet pawl and inthe plate. that the oisetting in the chuck arm plate is such as toprovide between the lower surface of the protractor plate and offsetportion 41 of the chuck arm plate (see Fig. 8) a space sufiicient toaccommodate the pawl 46 with an additional space below the pawlA toaccommodate the ball pivot, as clearly illustrated in the gure justreferred to. A spring plate 48, which is secured by screws 49 to theupper face of that .portion of the chuck arm plate which is justinwardly of the chuck arms and in the same plane therewith, constitutesa cover for the ratchet pawl and bears thereon so as to hold the pawland the portion of the chuck arm plate to which vit is pivoted to theball 41 in their proper relationship. A thumb-piece 50 is attached tothe end of the pawl at 50a just beyond the spring plate 48 and extendsinwardly'over -the protractor plate parallel thereto and upwardly andhas near its upper end a plunger-like extension 5l extending into acylindrical recess formed in the handle 28 into engagement with a coilspring 52 seated therein (see Fig. 6). This spring, therefore, acts onthe ratchet pawl so as to press the nose thereof toward the notched edgeof the holding plate 24 and enables the nose of the pawl to snap intothe notches when the protractor plate is rotated. It is to be noted thatthe thumb-piece is offset from the line of the chuck arm 39 andtherefore from the longer scale or ruler which is normally thehorizontal ruler. This arrangement I iind adds much to the convenienceofthe operator in manipulating the thumb-piece with his hand whichengages the handle 28, i. e., with -his hand on the top of the handleand his thumbon this oiset thumb-piece, he c a'n readily release thepawl from the notched holding plate and turn the protractor to thedesired extent.

Special attention is called to the facty I regard the ball pivot for theratchet pawl as important over an ordinary pin pivot inasmuch as itautomatically takes up for wear and through the medium of the overlyingspring plate the parts are held closelyv together but still with thedesired freedom of movement so far as the pawl is concerned irrespectiveof wear. Also with this type of pivot, together with the action of thespring plate, the ball and pawl may yield slightly with a shockabsorbing function in the event that the protractor is thrown around orrotated too fast and too roughly, thus reducing the likelihood ofinjury.

Asbefore stated, the notches are so located that. when the pawl snapsinto them the protractor will be held at the angles most commonlyemployed, such as 0, 30, 45, 60, etc. When the protractor is positionedat some other or intermediate angle and drafting work is done at thatangle, it is desirable that' the protractor plate be clamped in thatposition. For this purpose I employ a type of clamp previously used byme but arranged in a new way. In this in-v stance the clamp consists ofa stud 53 with a slot at its lower end and with a threaded shank engagedby a nut 54 having a wing 54a conveniently located for manipulation byone of the lingers of the operators hand engaging the handle. The slotat the lower end of the stud in this instance engages the innerunnotcl'ledv periphery of the annular portion of the holding plate 32(note particularly Fig. 7). `That is to say, this holding plate has anannular portion which lies immediately under the protractor plate andthe outer ,periphery of this holding plate is notched to receive thenose of the ratchet pawl and the inner periphery smooth so that it maybe engaged by the clamp. It will be understood, of course, that when theoperator turns the wing of the nut so as to screw the nut down theprotractor is clamped and when the wing is turned in the reversedirection it is released. A movement of a few degrees of the clamp nutis suflicient to clamp the protractor in place or to release it.

i I will next explain one of the most importantk features of theinvention, i. e., a new way of chucking the rulers and the constructionof both the chuck arms and rulers by which this is brought about. Asprotractors, particularly of drafting machines, have heretofore beenconstructed, the

chuck arms themselves were elevated from the drawing paper about thethickness of the rulers and the rulers were provided on their top sur-,

face at each end with a chuck which slid into a chuck receiving grooveformed on the under side of the chuck arm, each chuck bearing at threepoints in the groove of the chuck arm.v In this instance, the chuckingis done on the lower side of thev rulers instead of on the upper side asheretofore, the rulers having channels on their.

lower surface for this purpose, and each ruler has two or moreindividual chucks lying' in the channel and adapted to engage insuitably shaped chuck receiving slots of the chuck arm.

able with th'e arm, I prefer to provide three 75 4 chuck receiving slots55 in the relatively long chuck arm 39 and vtwo such slots in therelatively short arm 40, these slots being elongated slots on the centerlines of the chuck arms and extending transversely therethrough. Theslots 55 have tapered sides (Fig. 13) their narrower ends-- nearer theprotractor, are engaged by the chuckscarried 'by the rulers when theylatter are in clamping engagement with the chuck arms, the outermostslot in each arm need not be a full slot as is indicated in Fig. 13.With the chuck receiving slots formed as described, a novel form ofruler is employed. The construction of the ruler per se is not` claimedherein but forms the subject matter of a companion application SerialNo..526,913 led of even date herewith and hence,

only a brief description of the ruler will be given but the combinationofthe novelly constructed chuck arms with the channeled rulersl carryingindividual chucks on their under channeled side form important parts'ofthe present invention.

By reference to Fig. l0 it will be seen that the ruler has a metal core56 and this metal core is wholly encased in a non-metallic covering,such as celluloid or pyralin,. which is molded around the core by heatand pressure inthe manner described in my Patent No. 1,728,420. On theunder side of the ruler there is a channel 51 which in Width is morethan half the total width of the niler and which has 'slightly taperedsides. The crosssectional shape of the channel corresponds substantiallyto the cross-sectional shape of the chuck arm and when the chuck arm istted into the channel it substantially fills the same, the

such bearing surfaces.

aomaosaY i `undemuttmg of the side waus vof the slots. The

larger outer ends of these slots are somewhat wider than the chucks sothat in chucking theruler the chucks are placed into the wider porftions of the slots and then the ruler is pushed inwardly toward theprotractor and this causes the chucks to tightly engage the sides of theslots. With two chucks there are, therefore, four bearing surfaces(instead of three as heretofore) ,between the two chucks and the chuckarm, and with a ruler having three chucks there iwill be six It will beunderstood that if any chuck does not bear equally onthe twov sides, theproper bearing can be obtained by giving a slight adjustment to thechuck. The chucks preferably have the same thickness as the chuck armsand occupy lthe full depth of the slots. Obviously this permits the useofthinner and therefore lighter chuck arms than isthe case when chucksare employed which slide into 20 A grooves which extend only part waythrough As the chucking is done on the under side of I i the ruler, theupper side is left free, which yadds materially to the appearance andconvenience in using the rulers of the protractor. The chucking andunchucking is easy to accomplish, and the adjustment,` if necessary, canbe readily made so that the rulers are in true right-angularrelationship, and so that the different chucks wm 3 have the samechucking action in the slots of the chuck arms. A further importantadvantage of this method of chucking lies in the fact that there aremore points of engagement between the chucks and rulersand they aredistributed farther lengthwise of the rulers, this being particularlytrue of the longer rulers, resulting in a more secln'e holding effectand a greater stiffness and less lateral spring, particularly as aresult of lateral pressure applied to the ruler near its outer lowerside of the chuck arm then being flush with end. The fact that theholding surfaces of the or slightly above the lower surface of the rulerwhich engages the drawing. paper. understood that the non-metalliccovering covers the lower channeled side as well as the other portionsof the ruler.

Each ruler 'is providedfcentral'ly of the chan# neled. side with aplurality of chucks 58 the number of which corresponds to the number ofchuck receiving slots in the chuck arm which is` to receive the ruler,it being understood that ne of these chucks is adapted to be receivedinto each of the chuck receiving vslots of the chuck arm. These chucksare held up against the under side of the ruler centrally of the channelby screws 5$- which engage threaded holes formed in the chucks. Thesescrews pass transversely through the. ruler and have at their upper endsheads which fit in vopenings formed in the non-metallic .that'ffthisadjustment permits the chucks to be moved slightly both laterally andlengthwise of .the ruler, in fact universally, and the object is to geta perfect t between the-sides of the chuck and the side walls of.` thechuck receiving slots in the chuck arms. The opposite sides or edges ofthe chuck are tapered to conform to the taper-in the oppositelongitudinal vedges of the slots and the edges are slightly beveled toconform to the ItWllbev chucks are right at the screws which secure themto the-ruler instead of at a distancetherefrom obviates bending in thechucks, this bending occurring at times with chucks formerly used. Wherethe ruler has three chucks engaging the chuck arm, relative bendingbetween the chuck 'arm and ruler in the lspace between the innermost andoutermost chucks is eliminated because the intermediate chuck makes thechuck arm and ruler act as a unit where the bending stresses aregreatest.- .'I'he use of a plurality of chucks at each end of the rulerhas further advantages over a .single long chuck as the former arelighter, permitting the use of heavier and more durable metal. As thechuck arms also`may be made thinner, the rulers and protractor may bothbe made lighter when the present invention isutilized.

As before stated, the rulers engage the drawing 6 paper for their fulllength, and in order that the protractor may have a good bearing on thedrawing board beneath the handle and protractor plate, I prefer tosecure tothe bottom of the pro'- vprotractor is moved to and partiallybeyond the 7 edges of the paper on the drawing board there is lesslikelihood that the strip will pass beyond the paper and therefore lesslikelihood thatthe edge of the paper will be torn by the protractor inmoving it back onto the drawing.

vIt will thus be seen that the present invention resides in manyfeatures of the protractor, including the arrangement and manner ofconnecting the protractor plate, the holding plate and the chuck armplate, in the manner of supporting the ratchet pawl, the disposition ofthe thumb-piece therefor and the manner of supporting it, in thearrangement of the clamp with the inner periphery of'the notched plate,in the unitary form of the two chuck arms, and in the shape of thedifferent portions of the chuck arm plate, and in the new method of-chucking the rulers, including the means by which the chucking can beaccomplished on the lower side of the rulers through the medium of thechuck receiving slots and the separate chucks provided in the rulerchannel which receives the chuck arm of the protractor.

' While chucking in the channel on the lower side of the ruler as hereinexplained is highly desirable, nevertheless I do not desire to beconfined to that method of chucking. For example, the use of two or moreseparate and independently adjustable chucks at each end of the ruler isimportant whether bottom chucking or top chucking is employed. Ihesechucks might be secured on the top side of the ruler with the heads ofthe screws engaging the top wall of the channel and the chuck arm wouldextend over the ruler and engage themas before, but, of course with thatarrangement only part of the herein-mentioned advantages would beattained as compared with the preferred construction herein described.

It will be seen, therefore, without a repetition of the statement of theadvantages, that the objects of the invention enumerated in the earlypart of the specification are attained by the very novel protractorconstruction which I have herein illustrated, and while I have shown anddescribed only the preferred construction, it will be understood thatmodifications may be made in many of the details without departing fromthe spirit and scope of the invention, and I therefore aim in my claimsto cover all such modifications which come within the scope of theinvention, l

Having thus described my invention, I claim:

1. A protractor comprising a frame, a rotatable protractor plateconnected to said frame, a ratchet pawl for holding said protractor invarious positions, said pawl being provided with means for automaticallytaking up wear, and notches provided beneath the protractor plate insaid frame for engagement with said pawl.

2. In a protractor, a holding plate notched at various angles, agraduated protractor plate, means for rotatably connecting said platesincluding a single ball pivot between them, and means supported by saidprotractor plate for engaging said notches.

3. A protractor comprising a holding plate, a protractor plate abovesaid holding plate, a ball pivot between said plates, a ruler supportingmember connected to said protractor plate, and a spring arm on saidmember extending beneath said holding plate adapted to hold theprotractor plate and'holding plate in engagement with said ball pivot.

4. A protractor comprising a holding plate with a cut-out portion, aprotractor plate above said holding plate and pivoted thereto, and achuck arm plate beneath the holding plate and having a portion extendinginto the cut-out portion of the holding plate and securedto theprotractor plate.

i 5. A protractor comprising a holding plate having a substantiallyannular portion with an arm extending to the center thereof, aprotractor plate above the holding plate, a ball pivot'between said rarmand the center of the protractor plate. and a plate bearing chuck armsbelow said holding plate 'and secured to the protractor plate in theopening of the holding plate.

6. A protractor comprising a holding plate having a substantiallyannular portion with an arm extending" to the center thereof, aprotractor plate above the holding plate, a ball pivot between said armand the center of the protractor plate, a

plate bearing chuck arms secured to the protractor plate in the openingof the holding plate, and a spring arm connectedto said last men-Itioned plate adapted to hold the protractor plate and arm of the holdingplate in engagement with said ball pivot.

7. A protractor comprising. a frame, a member rotatably connected tosaid frame, a handle on said member coaxial therewith, a pawl forholding Ysaid thumb-piece being operatively connected with said pawl andin engagement with said handle.

8. A protractor comprising a frame, a member rotatably connected tosaid'frame, a pluralityr of rulers connected to said member. one oi saidrulers being longer than the other, a handle on said member coaxialtherewith, a pawl for holding said rotatable member in different angularpositions, a thumb-piece linearly movable in a direction transverse ofthe longitudinal axis of the long ruler, vsaid thumb-piece havingsliding engagement with said handle and being operatively connected tosaid pawl, and a spring in said han" dle acting on said thumb-piece.

9. In a drafting instrument, a protractor having a ruler supporting armprovided with a plurality of tapered chuck receiving slots.

10. In a drafting instrument, a protractor having' a ruler supportingarm, said arm having a longitudinally extending undercut chuck receivingslot extending therethrough.

11. In a drafting instrument, a protractor having a ruler supportingarm, said arm having a plurality of longitudinally extending undercutchuck receiving slots extending therethrough.

12. In a drafting instrument, the combination of a protractor having aruler supporting arm, a ruler having a channel adapted to receive theruler supporting arm, and means for chuckingA adjustably secured to theruler for chucking the ruler to the ruler supporting arm entirely withinthe channel.

14. In a drafting instrument, the combination of a protractor having amiler supporting arm provided with a plurality of chuck receiving slots,a ruler, and a plurality of separate chucks attached to the ruler andadapted to engage in the to the ruler supporting arm.

15.'In a drafting instrument, the combination of a protractor providedwith a ruler supporting arm having a plurality of chuck receiving slots,a ruler, and a pluralityof individually adjustable chucks attached tothe ruler adapted t0 engal'e in the slots andv act simultaneously inchucking' 17. A protractor assembly comprising a frame, l a memberconnected to said frame, a ruler supported by said member, and arectangular work engaging member having a large surface supported bysaid frame diagonally with respect to said ruler.

18. In-a drafting instrument the combination? of a parallel motion arm,a ruler supporting arm slots and act simultaneously in chucking theruler.

operatively connected to said parallel motion/arm, i a ruler having anaperture therein adapted to receive the ruler supporting arm, and meanswholly within said aperture for detachably securing said rulerlto saidruler supporting arm. '5 19. In a drafting instrument the combinationoi.' a parallel motion arm; a ruler having a chan' nel therein, a. rulersupporting arm operatively connected to said parallel motion arm withthe free end thereof positioned in said channel, and 10 a member withinsaid channel and attached to said ruler for connecting said ruler tosaid ruler supporting arm in tight gripping but separable relation.

20. In a drafting instrument, the combination 15 of a parallel motionarm, a ruler supporting member operatively connected to said parallelmotion arm, a ruler member having a channel adapted to receive the rulersupporting member. one of said members having an elongated `undercut 20chuckslot therein, a chuck secured to the other of said members andadapted to engage in said elongated undercut chuck slot in the other ofsaid members. V

CHARLES H. LI'I'ILE. 25

